While it is well known that adult listeners must be intensely aware of supra segmental (e.g., vowel duration, linguistic stress, etc.) factors of the speech code in order to understand speech, their is very little information about how the ability to perceive such factors develops in infancy and childhood. This research is designed to trace the development of the infant's ability to integrate supra segmental and segmental information in speech perception. A series of interrelated studies are proposed, to be conducted with 6 and 12-month-old infants using the Visually Reinforced Infant Speech Discrimination (VRISD) paradigm. The infant's capacities are assessed in the following areas: (1) perception of differential vowel duration; (2) the use of vowel duration as a subphonemic cue to facilitate discrimination of difficult to perceive segmental contrasts; (3) the detection and use of correlates of linguistic stress (increases in fundamental frequency, intensity and duration) to highlight difficult segmental distinctions; (4) perception of segmental changes in both short and long syllables; and (5) ease of discrimination of single vs. multi-syllabic speech sounds across two ages.